Canada's understanding of the "Controlled use" principle

Canada's understanding of the "Controlled use" principle

1. 
   The Canadian government's review of the experts' reports and answers to the questions posed by the Panel reveals that there is one crucial issue, which seems to override all other issues. This is the question of whether the application of the controlled use principle is feasible and credible in all stages in the life cycle of a product. While there is a reasonably high degree of agreement among experts that controlled use can be a reality in the mining and manufacturing sectors, serious doubts are expressed that controlled use can be applied in a few sectors of use  installation, maintenance and demolition. However, the basis for this view is not documented, except by Dr. Infante and Dr. Henderson.
   
2. 
   By "controlled use", the Canadian government means "stewardship" based on the total life cycle. This is outlined in the document The Mineral and Metals Policy of the Government of Canada: Partnerships for Sustainable Development.⁹⁷ With regard to asbestos, this "controlled use" is based on the following general principles:
   

• 
  Only the chrysotile variety is used;
  
• 
  only a limited number of well-defined product applications, where it has been demonstrated that they can be handled safely, are allowed (i.e. where the fibres are encapsulated in a matrix such as cement, bitumen, plastic, resin, etc.);⁹⁸ and
  
• 
  new product applications may be introduced only after a strict evaluation to ensure that a certain level of fibre release is not exceeded during its life cycle.
  

1. 
   With regard to the downstream use sectors, "controlled use" implies that all distributors/manufacturers of asbestos will be required to have an import permit. This permit will be withdrawn if the company does not meet the following commitments:
   

• 
  To distribute its products only to companies (users) licensed to purchase these products. Those companies must have workers trained and licensed to install products, and must be in compliance with regulations. Approved users shall not resell to third parties, and any unused materials must be returned to the manufacturer;
  
• 
  to provide a list of users of products to the responsible government agency;
  
• 
  to provide products cut to specification and to establish centres equipped to cut the products to size, and where persons cutting the products are trained and are licensed to work with asbestos; and
  
• 
  to police the downstream users in co-operation with the government. The product manufacturer visits, monitors and reports on the performance of the downstream users at regular intervals. There are penalties for failing to provide this product stewardship.
  

1. 
   While high-density products in most countries are not considered to pose any occupational or environmental health risk, disposal should only be undertaken by approved and appropriately trained persons.
   
2. 
   Dr. Infante's description of the permissible exposure limit for chrysotile asbestos, as well as programmes or standards that recommend or require specific engineering control, work practices, training and education and personal protective equipment to control exposures to asbestos corresponds, to some extent, to Canada's approach. Dr. Infante seems to suggest that because some workers do not comply with standards and regulations on controlled use in the United States, controlled use is not feasible. As explained in Appendix A on friction material and Appendix B on asbestos cement, the controlled use approach can minimize, if not eliminate, workers' non-compliance.⁹⁹
   
3. 
   Canada does not propose that any chrysotile products produced, sold or used without the implementation and enforcement of very stringent control procedures. Taking into account the types of products being manufactured and used in France at the time of the ban, Canada does not advocate re-introducing any product that cannot be handled according to the safety criteria outlined above. Canada is not advocating the introduction anywhere in the world of manufacturing facilities of products for which the technology does not exist to protect workers from exposure to chrysotile at levels where risks would be above epidemiologically based practical thresholds.
   
4. 
   The experts have indicated that the level of exposure is such that they are not concerned about asbestos-related disease for persons living in buildings containing chrysotile asbestos products, including friable insulation. As none of the chrysotile products that will be used in the future are friable, this conclusion would be further reinforced. If the procedures envisaged under the "controlled use" policy are followed by licensed practitioners, the public will not be placed under any practically determinable increased risk of disease as a result of the manufacture and use of chrysotile containing products. Unlike friable insulation products where janitorial staff, electricians, carpenters, and others may be required to work regularly in an environment where exposures to asbestos would occur, the nature of the high-density products will ensure that exposures are a much rarer event.
   
5. 
   Canada recognizes that the clock cannot be turned back. Friable mixed products produced in the past are now in place, and trades such as electricians or telephone engineers face situations where the potential health risk from exposure is considerably greater than any additional risk that new high-density chrysotile products would present. It is evident that the protection of workers who come into contact with friable products must be assured by the responsible jurisdictions through training in trade schools, appropriate information programmes by unions, and by governments and employers ensuring that the appropriate equipment and tools are made available to workers.¹⁰⁰
   
6. 
   Regarding high-density products, Canada believes that no less stringent measures should be required, even though the evidence shows that the risk from exposure to high-density chrysotile products is minuscule compared to the risk from friable products, in many cases containing mixtures of chrysotile and amphibole fibres. Furthermore, in the absence of sound scientific data to the contrary, the same criteria should be applied to the handling of all products in which respirable fibres, including asbestos substitutes, may be released.
   

2. International Standards

29. 
    None of the experts acknowledges that controlled-use of chrysotile asbestos cement products and other high-density chrysotile products stems from international standards. Dr. Infante even denies the existence of international standards on controlled-use of high-density chrysotile products. Canada wishes to remind the Panel that international standards, as the term is defined in the Agreement on Technical Barriers to Trade, do exist. Regulatory developments on asbestos fibres have been guided by ILO Convention 162 concerning Safety in the Use of Asbestos.¹⁰¹ ILO convention 162 provides for: (i) the prescription of adequate engineering controls and work practices; (ii) the prescription of special rules and procedures for the use of asbestos or certain types of asbestos or products containing asbestos or for certain work processes; (iii) where necessary to protect the health of workers and technically practicable, the replacement of asbestos or of certain types of asbestos by other materials or the use of alternative technology scientifically evaluated by the competent authorities as harmless or less harmful; and (iv) total or partial prohibition of the use of asbestos or of certain types of asbestos in certain work processes.¹⁰²
    
30. 
    The Code of Practice on Safety in the Use of Asbestos of the International Labour Office referred to by Canada in all its submissions is another international standard on controlled-use.¹⁰³ The objects of the Code are: (i) to prevent the risk of exposure to asbestos dust at work; (ii) to prevent harmful effects on the health of workers arising from exposure to asbestos dust; and (iii) to provide reasonably practicable control procedures and practices for minimising occupational exposure to asbestos dust. To do so, the Code gives detailed guidance on the limitation of exposure in respect of asbestos cement and friction materials. Finally, Canada has referred the Panel to International Standard ISO 7337: Asbestos Reinforced Cement Products  Guidelines for On-Site Work Practices.¹⁰⁴ This international standard gives guidelines for tools and working methods to be used on site with a view to maintaining the dust emission at the lowest practicable level. It applies to asbestos-cement products.
    
31. 
    The ILO Convention 162 and the Code of Practice on Safety in the use of chrysotile should be supplemented by a national policy on responsible use based on the recognition and acceptance of the principles that both international standards set forth.¹⁰⁵ As explained above, the objective of responsible use is to limit the handling of chrysotile to companies that comply with the national regulations or that have submitted action plans and formal commitments in writing with a view to bringing their activities into line with these regulations.
    

32. 
    The experts recognize that training could be achieved in the manufacturing sector, where there is a small and cohesive workforce, but assert without support that it cannot be achieved in the construction sector, where there is a large and non-cohesive workforce. Dr. Infante wrongly equates non-compliance with regulated training requirements to non-feasibility of training for controlled-use of chrysotile asbestos.¹⁰⁶
    
33. 
    In Europe, as in other countries, there are now requirements for training workers. In Canada, both levels of government require training at all workplaces. It is possible for training to be made available by industry. In fact, information and training is one of the most important elements of a company's preventive control programme. In line with the controls suggested at paragraphs ii.21 and ii.22, France could require through legislation that all construction workers handling asbestos products attend training sessions. France could also require that only designated, properly trained workers be allowed to work with those asbestos products that need to fall under a controlled regime.
    
34. 
    During manufacture, controls such as wet processes and exhaust ventilation, essentially eliminate all exposure. On the work site, process changes are reduced by the industry manufacturing products requiring no, or virtually no, modifications on site. The controlled use approach includes the use of pre-cut and pre-drilled asbestos cement products, and provides for designated locations where chrysotile asbestos cement sheets or pipes are cut and drilled and where the appropriate controls are in place. The monitoring process is similar to that for other workplaces: all complaints are submitted to governmental inspectors for evaluation. The supplier has the responsibility for ensuring that all companies to which they supply have in place the proper equipment and training to ensure safe use of the product throughout its life cycle. Finally, the removal of high-density chrysotile products is carried out in accordance with government codes.
    

35. 
    Both Dr. Henderson and Dr. Infante agree that, in many situations, when standards are properly applied, it is possible to maintain exposure below 0.1 f/ml. Also, as explained in Appendix A on the friction industry and Appendix B¹⁰⁷ on the asbestos cement industry, experience shows that a level below 0.1 f/ml can be achieved because the technology and work practices exist to control exposure during manufacture. No guarantee can be offered that there would never be a situation in which 0.1 f/ml might be exceeded as a peak exposure. However, there is no evidence that occasional peak exposures increase the risk of lung cancer or mesothelioma in chrysotile exposed workers. For example, the health experience of brake mechanics, i.e. no evidence of an increased risk of mesothelioma or lung cancer, is based on exposures that involved peak exposures, such as occurred during the blowing out of brake wear debris and the occasional grinding of brake linings. These operations involved short exposures above 0.1 fml. The actual concentrations associated with various tasks have been reported by Kauppinen and Korhonen,¹⁰⁸ and by Rödelsperger.¹⁰⁹ In spite of these short-term peak exposures, the average exposure of auto mechanics was less than 0.05 fml.
    
36. 
    A person repairing their own brakes periodically nowadays (using disc brake pads mainly) would have extremely low cumulative exposures compared to full time auto mechanics and there is no reason for them to have any, even short term, exposures exceeding 0.1 fml. The risks associated with cumulative exposure to chrysotile at these levels would not be epidemiologically detectable for handymen handling friction or asbestos cement products.
    
37. 
    Rödelsperger¹¹⁰ made dust measurements on about 40 buildings sites in Germany. He reported peak exposures of more than 100 fml in the vicinity of a grinding machine used to cut asbestos cement sheets. However, when he used the standardized work histories of 61 roofers, who had a mean duration of exposure of 16 years, he found that their mean cumulative exposure was 1.6 fibre-yearsml. These measurements were made 20 or more years ago, with the products and technology available then and for regular construction workers. It is evident that even under these circumstances, lifetime cumulative exposures were low. Thus, a handyman, even if he did not take proper precautions would still have a low cumulative fibre exposure because peak exposures are of short duration and he would be at a very low, undetectable risk of health effects.
    
38. 
    It is generally agreed that at the levels of exposure associated with the use of the modern high-density products, they would not even put a full-time worker at increased risk of asbestosis and, therefore, this would not be of concern for a handyman working occasionally with the product. It has been amply demonstrated that the risk of lung cancer increases with increasing cumulative lifetime exposure that combines duration and level of exposure. A person exposed at 0.1 fml for 40 years has a cumulative lifetime exposure of 4 fml-years. If that person worked on a project only once each week for four hours for 40 years, he would not achieve the same lifetime exposure unless he was exposed to 1 fml continuously for the four hours of exposure every time he was exposed for 40 years. Thus occasional peak exposures of a few minutes contribute very little to cumulative lifetime exposure which is important in evaluating the risk of chronic diseases such as lung cancer or mesothelioma.
    
39. 
    Gardner¹¹¹ found no increased risk of lung cancer or other asbestos-related disease in a chrysotile asbestos cement plant where exposures were less than 1 fml. This was in a cohort of workers employed between 1941 and 1983. It is evident that any risk would have been well below the detection limit at 0.1 fml. A study of chrysotile cement production workers by Thomas¹¹² and Neuberger & Kundi¹¹³ identified no chrysotile-related increased risk of lung cancer and Weill,¹¹⁴ while reporting an increased risk of lung cancer in asbestos cement workers, found the increased risk only in those with asbestosis. In this study, there was little evidence of asbestosis below 30-40 fml-years of exposure. This is about 0,75-1 fml continuous exposure for 40 years. Thus, there is little evidence to support a detectable increase in risk of lung cancer in workers with a 40 years cumulative lifetime exposure at 4 fml-years.
    
40. 
    Any risk estimates obtained by linear extrapolation from high exposures to such low exposures are somewhat hypothetical and both Lash¹¹⁵ and Camus¹¹⁶ have shown that the risk estimates made by the U.S. Government have overestimated lung cancer risks.
    

41. 
    Canada disagrees with the views of Dr. Henderson¹¹⁷ and Dr. Infante that controlled use of chrysotile asbestos is not feasible for workers involved in the construction trade and that service and maintenance workers such as carpenters, plumbers, and electricians will experience peaks of exposures to asbestos that place them at risk. The nature of high-density chrysotile asbestos products is such that few of the trades listed above will ever need to work on the products, with the possible exception of demolition workers. Again, there is evidence that during demolition exposure concentrations associated with chrysotile asbestos cement products is very low.¹¹⁸ Today, with chrysotile cement products and controlled use procedures, health risks become insignificant.
    
42. 
    Recommended installation methods can eliminate the need to cut or drill into chrysotile-based products at construction sites, since those products are distributed in a variety of pre-cut and pre-drilled sizes, according to buyers' specifications. In fact, many asbestos cement products are pre-formed ready for use. They are factory-made to the correct size and shape including holes so that a minimum of on-site preparations is needed. Once installed, chrysotile asbestos cement pipes are below ground and pose no risk to workers. Even if dug up, they pose no risks unless comminuted, ground or sawed, and, when this is necessary, the use of appropriate tools and controls will keep the release of dust and exposure well within the level considered safe by the WHO. Chrysotile asbestos cement sheets are used for roofing and exterior building walls. Once installed, there is no need to modify the roof until the life of the product is over. Similarly, there is no need to modify chrysotile asbestos sheets used as walls once they have been installed. The product can be painted without fibre release.
    
43. 
    Chrysotile cement products are unlikely to release fibres into the environment or breathing zones of workers such as janitors, plumbers, electricians, repair men, etc., unless these workers have to actually cut or drill the product. Unlike insulation products, there will rarely be a need for anyone to perforate, saw, or grind installed chrysotile cement products. Where cutting or drilling is required, hand tools and low speed power tools are recommended in combination with wetting to keep dust levels to a minimum. Dust levels for various types of on-site working have been measured both in laboratories and in the field and these facts showed that risks could be maintained below detection limit.
    

44. 
    Dr. de Klerk and Dr. Musk wrote that efficiency of controlled-use in the case of home handymen is outside their area of expertise. However, both Dr. Henderson and Dr. Infante have concluded that it is not possible to control exposure to chrysotile asbestos high-density products in non-occupational circumstances (occasional interventions by home handymen). Neither bases his conclusion on data. Dr. Henderson adds to his answer that although such risks are not quantifiable because of absence of data, these risks must be very small for lung cancer and mesothelioma, and non-existent for asbestosis.
    
45. 
    Controlled use will reduce and even eliminate risks. The risk of chrysotile-related health effects is tied to cumulative exposure, that is, duration and level of exposure. Rarely will an individual under non‑occupational circumstances achieve the exposure of a full-time worker. Occasional uncontrolled exposures for a handyman would not result in appreciable cumulative exposure. Data published by Brown¹¹⁹ showed time-weighted average (TWA) levels during demolition of weathered asbestos-cement roofing between 0.3 and 0.6 f/ml. One can likely guess that a handyman would not practice such an activity more than 40 hours in 25 years. This would average out to a TWA of 0.015 f/ml for the year of this activity, and a TWA of 0.0006 f/ml each year of the worker's adult life. This is 1 million times less than past asbestos workers are. It is equivalent to exposure levels in schools containing ACM.¹²⁰
    
46. 
    Based on INSERM¹²¹ and HEI-AR risk tables, which are based on mixed asbestos exposures, the resulting lifetime cancer risk would be between 10 and 20 in a million depending on the time occurrence of this exposure scenario. More accurately however, the lifetime risk would be near zero per million, based on chrysotile friction workers who were exposed to similar fibres (species and dimension wise), and about 1 in a million, based on the risks of past chrysotile miners and millers. The casual user of a high density product, even if the product were weathered, is not likely to be at any increased risk of an asbestos related disease. If the supplier follows through on the requirements of controlled use, the casual purchase of chrysotile asbestos-cement products by the handyman will not be possible. However, there is probably no way of stopping any individual from doing something to any product if they can obtain it. This is a problem that exists for any product many of which pose serious health risks if abused.
    

1. 
   Canada respectfully disputes the conclusions of the experts regarding the risk from substitute fibres, and with respect to one expert, the ability of substitutes to serve as suitable replacements to chrysotile. Canada notes that the treatment of the issue by two of the experts is terse, comprising only several sentences. To their credit, Drs. de Klerk and Musk indicate that the use and control of substitute fibres is not within their areas of special expertise. They offer some responses nonetheless. Canada is concerned, in particular, by their lack of familiarity with the relevant studies and actual modes of production, use and disposal of substitute fibres. For example, they apparently are unaware of research conclusively demonstrating the significant health risks from exposure to refractory ceramic fibres (RCF), which are discussed below.
   
2. 
   This concern applies to Dr. Infante as well. Dr. Infante further appears unaware of (or ignores) recent research demonstrating that chrysotile is less biopersistent than many substitute fibres. Dr. Infante also ignores the population the experts agree are most at risk from exposure to any fibre – tradesmen – when he concludes (without support or, even, explanation, Canada notes) that the "nature of the production process makes substitutes more amenable to control than asbestos fibres." Assuming he is not again conflating chrysotile with amphiboles when referring to "asbestos," his point, were it true, would be irrelevant. The experts agree that chrysotile and chrysotile products can be safely mined and produced. The key is exposure to tradesmen. And, for that exposure, no rationale exists suggesting that the ability to impose effective controls differs based on the type of the fibre.
   
3. 
   Dr. Henderson, for his part, recognises that, as with all fibres, the pathogenicity of substitutes is defined by the "3Ds" (dimension, dose, durability). He seems also to understand that, due to the (lack of) historical use of substitutes, we cannot fully know the risks of using them.¹²² However, he then seems to ignore the importance of these facts.
   
4. 
   All of the experts fail to take into account several very important factors. First, the chrysotile products at issue in this proceeding are quite few. Second, the exposure levels during the manufacture, use and disposal of these products are extremely low. Third, the data demonstrate that these few products have been and can be used without detectable health effects in humans. Moreover, in order to assess whether a substitute is safer to use than chrysotile in a product: (i) it is fundamental that the characteristics of the fibres being compared be those of the fibres as they are used in the product or as they are released from the product throughout the product's lifecycle; (ii) it is essential that data on at least the key parameters (exposure, biopersistence and dimensions) be available to make this assessment. Unfortunately, the experts have not addressed these topics. In short, the experts have based their opinions on very limited, if any, data. While the experts reach conclusions that various substitutes (PVA fibres, glass fibres, cellulose and para-aramid fibres) are safer to use than chrysotile, they provide no systematic comparison of risks and very limited, questionable scientific data in support of their opinions.
   
5. 
   Canada presents below a survey of the studies and concepts that the experts ignored. These studies give a picture of risks from substitute fibres starkly different from that suggested by the Panel's experts. As demonstrated below, the situation concerning risk from substitute materials is as Canada set out in its factual arguments.¹²³
   

1. The Fibres to Compare

1. 
   Experimental data for a wide range of fibres have shown that the physical characteristics (diameters, lengths, density) of fibres are important in determining their respirability, when they are deposited in the respiratory system, and their capacity to induce fibrosis and cancers. Further, the risk of effects also depends on dose (exposure). Thus, differences in the risk of disease in various industrial sectors would be expected to occur because of differences in these, as well as other factors. As the characteristics of chrysotile and any substitute fibres are likely to be dictated by the product in which they are used, it is not appropriate to assess the risks associated with friction products or asbestos cement products using data from other industrial sectors. The data that should be available and used for the purpose of comparing risks should be those for the fibres as used in the specific products under review. Canada's presentation proceeds on this basis.
   
2. 
   Davis¹²⁴ pointed out that while materials like wool, cellulose and other fibres have in some cases been used for many years, they are now being used in quite different applications, about which knowledge is very limited. As a consequence, the characteristics of the fibres used in the newer applications may not be the same as those in the conventional products manufactured in the past. Such changes can modify the respirability and biological activity of the materials. There is a further complication for substitutes that is not addressed by the experts. This is the fact that substitution does not always involve replacement of chrysotile by a single fibre, but often by several different materials or substitute fibres. For example, cocktails of fibres are needed to meet technical requirements in friction products. In addition, when substituting for chrysotile, other materials such as silica or other fibres, fire retardants or biocides must often be added. These agents may themselves be toxic or carcinogenic, and may act synergistically.
   

2. The Outcomes to be Measured

1. 
   While it is reasonable to compare the risks of lung cancer and mesothelioma between the various fibre types, it must be remembered that different sized fibres may lead to fibre deposition at different locations in the respiratory system. For example, if more fibres of one material than another are likely to be deposited in the nasal passages, one should consider the possibility of an increased frequency of nasal cancer in evaluating the substitute. Dr. Infante mentioned the increased risk of nasal cancer in woodworkers, which has been well established.¹²⁵ This might raise a question concerning the sources of the cellulose used as a substitute and whether controls are in place to avoid exposure to cellulose from woods that have caused such cancers. Also, some materials may cause dangerous allergic responses. Certain glass fibres cause skin irritation. Harrison¹²⁶ notes that there are indications of an accumulation of oligomers in the kidney in some circumstances, so that attention should be given to the molecular weight of PVA used "especially if a smaller diameter material were to be produced."
   
2. 
   In considering risks, the composition of the dusts and fibres to which workers are exposed when handling the "raw substitute" materials, manufacturing the product, cutting, grinding, manipulating or disposing of the product also must be considered. For example, it is important to know whether the fibres of para-aramid, PVA or cellulose are opened (fibrillised) or comminuted during preparation or manufacture of the product? Does manipulation, sawing or drilling of the product give rise to narrower diameter respirable "fibres" such as result with polyester fibres during weaving? Do these fibre fragments have biological significance? What are actual use concentrations? It must be remembered throughout that there exists a substantial body of information concerning chrysotile. Unfortunately, in the case of substitutes, there are rarely any human epidemiological data available and even experimental data are limited. Perhaps this fact led Dr. de Klerk to conclude that "[G]iven the comparative lack of knowledge about the health effects of substitute materials, the continued use of chrysotile under [controlled] circumstances seems sensible.¹²⁷
   

3. The Essential Data

1. 
   The data that need to be compared in an evaluation of the relative safety of chrysotile and substitutes include the following:
   

• 
  Epidemiological data that provide direct evidence of the risks associated with the products.
  
• 
  Experimental data by inoculation of fibres or by inhalation experiments in experimental animals.
  
• 
  Dimensions of fibres in the respirable airborne dust during the manufacture of the product.
  
• 
  Dimensions of fibres in the respirable airborne dust during the use of products containing the fibre.
  
• 
  Dimensions of fibres in the lungs of workers engaged in the manufacture of products containing the fibre.
  
• 
  Dimensions of fibres in the lungs of persons exposed during the use of products containing the fibre.
  
• 
  Dimensions of fibres in the respirable airborne dust and in the lungs following exposure during the disposal of the fibre or products.
  
• 
  The biopersistence of the fibres in humans and animals.
  
• 
  The cumulative exposure (i.e.: concentration x time) of workers engaged in all phases of manufacture, use and disposal of the product.
  
• 
  Data on alterations or modification of the fibres chemically, physically and biologically during their life cycle that might affect their potential to cause health effects.
  

57. 
    Even if one were to narrow the requirements to a smaller number of key parameters such as fibre dimensions, biopersistence and exposure-response, the available data are still inadequate to provide a credible basis for an adequate comparison. Thus, the unqualified wholesale affirmation that "substitutes are safer than chrysotile" is not well founded and potentially very dangerous. For example, prior to the finding of a very high risk of mesothelioma for persons exposed to very low concentrations of fibrous zeolite erionite in Turkey, there had been no indications world-wide that such fibres might after 30 years from first exposure at such very low levels produce such a high rate of mesotheliomas in humans. In South Africa, crocidolite had been used for about 60 years before Wagner¹²⁸ reported that mesotheliomas were associated with crocidolite exposure. In humans, mesotheliomas do not occur until 40-60 years after first exposure. Thus, caution is needed in the absence of data regarding substitute fibres. As one expert stated: "better the devil you know" than the devil you do not know.¹²⁹
    

1. Dimensions

1. 
   The experts present no data that show that the dimensions of all fibrous substitutes are outside the respirable size range during the substitute product's lifecycle. This is because no such data exist.
   

2. PVA & Aramid Fibres

1. 
   Views from the experts appear to be mixed. Dr. Henderson quotes Harrison's review stating that PVA and aramid fibres are too large to be respirable. Dr. de Klerk states that all substitutes except glass (cellulose, aramid, PVA) produce a larger proportion of non-respirable fibres than chrysotile but respirable fibres are similar for all substances. Dr. Musk offers no opinion. Dr. Infante states that PVA fibres are "mostly" in the size range 10-16 µm and aramid fibres 10-12 µm. However, he notes, quite correctly, that, as mentioned below, the aramid fibres can and do split into fibrils of about 0.2 µm in diameter.
   
2. 
   In assessing fibre respirability, none of the experts accounts for the fact that respirability depends on density as well as fibre diameter. The densities of PVA and para-aramid fibres are both considerably less that that of chrysotile. This means that much larger diameter substitute fibres would be respirable. In fact, the upper limits of diameters that are respirable for these fibres, as reported by Harrison¹³⁰, are approximately 7 µm and 6-7 µm respectively. The equivalent upper level diameter for chrysotile is about 3-3.5 µm. Thus, fibres of much greater diameter can penetrate into the alveolar region of the lung. A review of the available information in the literature is that there is a general opinion without data that the respirable fraction of PVA fibres is small. However, there do not appear to be any data on the dimensions of airborne fibres during mixing with cement or other materials, or as released from the products during processing and use.
   

3. Glass and Cellulose Fibres

1. 
   As far as cellulose and glass fibres are concerned, none of the experts provided any actual measurement data on the sizes or respirability of the fibres. Also, the dimensions of fibres at various stages of the processing, use and disposal of cellulose have not been reported. The actual dimensions of fibres in the airborne dust will depend on the specific glass fibres used and how they were prepared.
   

1. Biopersistence

   1. 
      It is well known that biopersistence is a key parameter. Indeed, the human evidence for chrysotile indicates that it is likely to be one of the main reasons why chrysotile is less dangerous than the amphiboles in respect to mesothelioma risk. This is clearly recognized by three of the four experts, as well as by INSERM.¹³¹
      

2. Cellulose

   1. 
      Drs. Infante, Henderson and de Klerk recognise that cellulose is durable in the lung. In fact, the data show that some cellulose fibres have half lives of about 1000 days in the lung, which are many times longer than even those published data for amphibole fibres, much less chrysotile fibres.¹³²
      

3. PVA

   1. 
      Dr. Musk and Dr. Henderson had no comment on PVA durability. Dr. de Klerk presented no data, but expressed the view that PVA was less durable than chrysotile. Davis, in a review in 1998, found no published data on the biopersistence of PVA fibres. Data was not published until 1999, when Harrison [1999] reported that PVA "will degrade very slowly, if at all in the lung."¹³³ There do not appear to have been any systematic studies of the biopersistence of PVA fibres, a crucial parameter in assessing the hazard associated with PVA fibres.
      

4. Para-aramid Fibres

   1. 
      Based on a study by Searl,¹³⁴ who compared chrysotile and para-aramid fibres, the general view of the experts is that para-aramid fibres are less biopersistent. However, Searl failed to check the lung tissue to confirm that the retained fibres were chrysotile. Based on studies using a standard protocol, Dr. David Bernstein has found that the biopersistence of chrysotile is in fact less than that of para-aramid fibres.¹³⁵
      

5. Glass Fibres

   1. 
      Drs. Musk, de Klerk and Henderson presented no data on the biopersistence of glass fibres. Dr. Infante, without identifying the specific glass fibres, reports that glass fibres are less biopersistent than chrysotile. In fact, the recent work by Dr. Bernstein, in which the same protocol was used as for synthetic fibres, found that long [i.e.: > 20um] pure chrysotile fibres are removed from the lung faster than most, if not all, of the glass fibres reported in the published literature.¹³⁶
      

6. Chrysotile

   1. 
      As far as chrysotile is concerned, it is well accepted that chrysotile is readily removed from the lung. This is why the lungs of chrysotile millers and miners, exposed to chrysotile, have been found at autopsy to contain more tremolite (an amphibole asbestos mineral) than chrysotile.¹³⁷ The chrysotile cleared, but the tremolite fibres remained in the lung because of their much greater biopersistence. There are various estimates of the half time for chrysotile clearance. Oberdöerster¹³⁸ studied baboons and estimated a 90-110 day half time for chrysotile fibres. The study by Searl was mentioned above. The estimates by Dr. Bernstein are even shorter (< 10 days).¹³⁹ For direct comparison purposes, the clearance rates for fibres in the same ranges of dimensions must be studied. In addition, it is crucial that the fibres be tested using the same methodology. The studies by Bernstein best fit these criteria and show that, size for size, chrysotile has a very short half-life.
      

1. Exposure-Response

1. 
   In the absence of exposure-response data, it is not possible to quantify the risks associated with the various fibres. The question to be addressed is not: is one material more dusty than another? Nor is it: is the concentration higher when working with one material compared to another? Rather, the question that must be asked is: what is the risk for workers manufacturing or using the product? The decision on which fibre is safer has to be made on the basis of an assessment of the risk of disease for workers when manufacturing and using a product containing chrysotile compared to that when manufacturing and using the same product containing the substitute when subjected to the same or equivalent handling.
   
2. 
   Three sources of data might be considered: experimental animal studies; human (epidemiological) studies; and in vitro studies. The latter (in vitro) are of little value for estimating risk as they only involve tests of, for example, biological activity in cells isolated from the processes which occur in a complete organism. Thus, they are an inadequate basis of comparison to the effects of inhalation on animals, much less humans.
   

2. Animal Studies

1. 
   The first approach involves the exposure of animals to fibres of well-defined characteristics and concentrations by inhalation and following them for their lifetimes. Such studies have been done for a wide range of synthetic mineral fibres. Problems with this approach are many, as has been demonstrated in the considerable work done in recent years on synthetic mineral fibres. First, the animal species may have a limit on the size of fibre that it can inspire. Second, there are marked differences in the sensitivity of different animal species. For example, a refractory ceramic fibre (RCF) which produced one or two mesotheliomas in rats, produced mesotheliomas in 40 per cent of the hamsters exposed. Third, the lifetime of rats is about two years. In order to produce an effect within the lifetime of the animals they are subject to enormous exposures. Such exposures can produce the abnormal situation of lung overload so that the real reason for any biological effect is not clear. Fourth, an animal must produce an effect within two years (before it dies of natural causes). If biopersistence is important, fibres that are readily removed in humans over the course of a human's life are not removed from the lung of an experimental animal because of the high exposures and shorter life. Fifth, the interpretation of much of the experimental work must be done with caution, because until recently, fibre exposures were reported on mass not number basis. As the materials tested can have quite different dimensions, the same mass can lead to exposures involving considerably different concentrations of fibres on a number basis.
   

3. PVA

1. 
   There are no studies relating the long-term effects of exposure to PVA fibres.
   

1. Cellulose

   1. 
      Studies that have been done with cellulose have shown that it initiates a severe inflammatory response¹⁴⁰ and fibrosis.¹⁴¹ Unfortunately, no chronic exposure data have been published.
      

2. Glass Fibres

   1. 
      While there have been many studies of glass fibres, the only study in which the same methodology was applied to the study of synthetic mineral fibres and chrysotile asbestos is that of Hesterberg.¹⁴² He found that while there is an increased risk of lung cancer identified at high concentrations (as for glass and other fibres) the animal data suggest that at low level exposure, the risk associated with the chrysotile exposure is considerably less than that associated with the synthetic mineral fibres tested.
      

3. Para-aramid Fibres

   1. 
      While in recent years the information base concerning aramid fibres has increased greatly, there remain several issues. The only data are those derived from experimental studies in animals. While studies of biopersistence suggest that long fibres are shortened by enzymes in the lungs of animal experiments (Searl) and hence removed from the lung, the situation in humans is not known. Two researchers (Davis¹⁴³ and Pott¹⁴⁴) have produced mesotheliomas by intra-peritoneal injection of these fibres, so their potential to produce mesotheliomas cannot be dismissed. The interpretation of "proliferative keratin cysts" observed during inhalation experiments remains unclear.¹⁴⁵ Minty et al., in a criteria document for an occupational exposure limit (OEL) in the UK, summarized what was known about the para-aramid fibres at that time and drew several parallels with chrysotile. For example they state that "[T]he balance of evidence suggests that respirable aramid fibres possess a low potential to produce mesothelioma which is likely to be at least as low as with chrysotile.¹⁴⁶
      
   2. 
      Referring to chrysotile, they conclude that mesothelioma "would only be detectable following very heavy and prolonged exposures." The recent evidence that the mesothelioma risk for chrysotile miners and millers is associated with tremolite, will render the threshold of mesothelioma for downstream workers even more remote. These authors considered a clear no-effect level of 2.5 f/ml for pulmonary toxicity and a recommended OEL of 0.5 f/ml to allow for "uncertainties in interspecies differences."
      

4. Epidemiological Data

1. 
   Drs. Musk, de Klerk, Henderson and Infante did not identify any epidemiological studies of PVA fibre workers. In fact, there is one study involving a small number of PVA fibre production workers (about 400 exposed employees).¹⁴⁷ Even though the length of exposure thus far is quite short, already two lung cancer deaths have occurred in the cohort to date. Clearly a much longer follow-up is needed. Regarding mesothelioma, it must be noted that with such a small population, even if half were dead and there were one mesothelioma, the risk would be 0.5 per cent which is more than the risk of mesothelioma found in Quebec miners and millers exposed to tremolite contaminated chrysotile. (Also, the Panel should note that there were no mesotheliomas among 1267 deaths in chrysotile exposed friction product manufacturing workers exposed to chrysotile.) Thus, this study cannot detect either mesothelioma or lung cancer risks as low as at that already known for chrysotile. Clearly, there are no human data on which to assess risk to conclude that the risk is less than it is for chrysotile either per f/ml of exposure or globally from work with products manufactured using PVA fibres.
   

2. 
   Dr. Infante states that there are three studies in which cellulose exposures have been investigated, but he does not identify them. The other two experts do not suggest any epidemiological data. Studies in which there is no overall increase in mortality from lung cancer are not adequate to investigate the risk of exposure. To assess this risk, the relationship between lung cancer and cellulose fibre exposures on a per fibre basis must be, but has not been, examined.